1. Field of Invention
The systems and methods of the invention are directed to distributed applications such as sensor networks.
2. Description of Related Art
The U.S. Patent Application Publication No. 2002/000920 discloses detection and maintenance of moving vehicle data in an array of sensors. All vehicles are identified at a fixed entry point and are sensed by only a single sensor at a time.
U.S. Pat. No. 6,366,913 discloses techniques for dynamic maintenance of group membership based on time-varying attributes, including position. The techniques operate through a centralized directory server.
U.S. Pat. No. 6,275,847 discloses a self-configuring distributed processing system which is pre-configured into cells.
U.S. Patent Application Publication No. 2002/0057340 discloses an integrated fixed and/or wireless network for monitoring and processing remote indoor local movable objects where an object database or functionally equivalent data structure is provided in digital storage and is accessible to control software that dynamically stores one or more positional and relative movements, as well as optional and associated map data.
U.S. Patent Application Publication No. 2002/0103911 discloses the idea of a moving information bubble.
As processor and networking technology increase in capability and decrease in price, large networks of geographically-distributed devices become practical where one or more devices are assigned responsibility for nearby physical phenomena. These phenomena may be measured using sensors nodes, which may affect the entities they measure through actuators, or may simply be assigned computational responsibility for the phenomena. A sensor node typically includes one or more sensors of the same type or of different types, such as, for example, acoustic and/or seismic, an associated processor and a transceiver. These networks may be dynamic in nature in the sense that both the devices, that is the nodes, and the entities may be mobile. New entities may appear, that is be detected, within the network, may move, thereby changing the responsible sensor nodes, or may disappear entirely.
Known systems of this type have moved all of the sensor data to central or pre-assigned regional aggregation sites and have not allowed the group of active nodes to vary according to current estimates of the position and extent of the phenomenon. Scalability and latency generally rule out use of centralized approaches for very high node-count, high phenomenon-count, or very widely-distributed systems, and region-based approaches with fixed aggregation centers are inflexible and often require complex multilayered overlapping regions to work properly. Wireless sensor networks are particularly ill-suited to centralization because of their limited battery power, and nodes close to aggregation centers must handle a relatively larger quantity of messages and tend to run out of power early, resulting in system failure. Fixed architectures also tend to concentrate most of the computational work at a single node, which is a highly inefficient use of a system with hundreds or thousands of nodes, and results in unnecessary latency.
Concurrent with these developments is work on data centric ad hoc networking, such as disclosed in Yu, et al., UCLA Computer Science Department Technical Report, UCLA/csd-tr-01-0023, May 2001. These systems allow data to be disseminated according to attributes of the local nodes in a publish-subscribe type of architecture. However, this has been expensive to use in large sensor networks because it requires flooding each time a subscription is changed. This approach has been used in several sensor network architectures to either efficiently send sensor data to a central node despite unreliable links and failing intermediate nodes or to set up fixed local groups. Still, new capabilities such as geographical routing, disclosed in the aforementioned Yu et al. publication, now allow data to be efficiently geographically routed in a dynamic fashion, changing the active region on a per message basis.
Sensor networks are subject to certain resource constraints such, as, for example, limited onboard stored energy (e.g., battery) or limited power availability (as with solar power) and limited network communication bandwidth. Networked sensor nodes typically operate untethered and have a microprocessor with limited memory for signal processing and task scheduling. Sensor nodes may be equipped with various types of sensors including, for example, acoustic microphone arrays, video and/or still cameras, Infrared, seismic and/or magnetic sensing devices. Sensor nodes also communicate wirelessly with a number of other nodes within communication range.